1. Field of the Invention
This invention relates to a dispenser and more particularly to a technique effectively applicable to a dispenser which applies a material such as creamy solder and an adhesive onto an article such as a substrate used in a semiconductor technique, wherein a vertically moving stroke of a needle of the dispenser is controlled with high precision and conditions for discharging the material to be applied are controllable in accordance with remaining amount of the material.
2. Related Art Statement
In an automatic assembly line used in producing semiconductors for example, such an arrangement is adopted that, when electronic parts such as a chip resistor, a capacitor and a packaged IC are mounted onto a substrate formed thereon with a circuit pattern, creamy solder is applied on predetermined positions of the substrate by use of a dispenser or the like, and then, electronic parts are automatically mounted using a chip mounter and the like.
The dispenser used in such an assembly line comprises a needle having a predetermined inner diameter and fixed at the forward end of the dispenser, a syringe for storing therein creamy solder, and a plunger housed in the syringe in an upwardly and downwardly movable manner for discharging the creamy solder by a displacement of the plunger toward the needle. The creamy solder is pushed out of the plunger due to this displacement of the plunger and discharged from the forward end of the needle.
As a driving mechanism of this dispenser, a hydraulic equipment such as an air cylinder has been used, and suction and exhaust of fluidal pressure into and out of the air cylinder cause a piston rod to move up and down, whereby a syringe fixed to the piston rod is moved up and down within a predetermined range.
In the above-described conventional technique, since the vertical movement of the syringe is controlled by suction and exhaust of the fluidal pressure into and out of the air cylinder, quick responsiveness is not obtained when the fluidal pressure is supplied to or exhausted from a fluid chamber of the air cylinder to cause displacement of the piston rod for making the syringe move up and down.
Further, it is impossible to obtain a satisfactory clearance precision between the forward end of the needle and the substrate in the stroke range of the upward and downward movements of the syringe, even if high degree of positioning precision is required for applying solder.
Furthermore, in the automatic assembly line, it is necessary to detect the decrease of the material to be applied, to replenish the material or to exchange an old syringe for new one filled with the material, before the material in the syringe is used up. In this management of the material to be applied, such a method, for example, is adopted that detection is made with the naked eye of an operator or by estimating the used amount based on the time elapsed and the scheduled amount of using the material.
However, in the above-described management by the detection method with the naked eye of the operator or the detection method of time-based estimation, considerable labor of the operator is required and inferior products tend to be produced due to uncertainty of detection.